The present invention relates to line surge protection for telephone equipment and, more particularly, to a unitary line surge protector for removable connection to an existing block and jack assembly of a main distribution frame of a telephone exchange system to protect telephone equipment from line surges on any individual telephone lines.
Telephone lines coming into a telephone office are typically terminated on a main distribution frame and are extended from the frame to the telephone office equipment. The lines are terminated on block and jack assemblies which provide connecting terminals as well as test jacks on the main distribution frame.
One block and jack assembly commonly used to connect incoming lines to telephone office equipment is referred to as the 444-type connector. This type of block and jack assembly is designed to handle the interconnection of two sets of two-wire pair lines with provision for the line current to pass through normally closed jacks that may be opened for test purposes. A mounting plate attached to the main distribution frame supports a large number of the 444-type assemblies in stacked relation.
The use of this simplified 444-type block and jack assembly was instituted as a space and cost saving measure when it was found that both protector blocks and heat coils could be eliminated at the main distribution frame. As a result, the telephone office may employ countless 444-type block and jack assemblies stacked in close proximity without any form of fault protection. It has been found, however, that with increased telephone system complexity and more diversified use, there exists a need to provide line surge protection at the main distribution frame in order to protect the telephone office equipment from overcurrent and/or overvoltage conditions (e.g. lightning) that might not otherwise be dissipated in the system. This is made difficult, of course, in the case of the main distribution frame using the 444-type block and jack assembly since one of the design criteria for this assembly was that protection of this type was not needed. Accordingly, the tightly packed terminal blocks and test jacks mitigate against an easy solution to the problem of protection at the main distribution frame.
Accordingly, it is an object of the present invention to provide a novel line surge protector for 444-type block and jack assemblies mounted in stacked relation on a main telephone distribution frame wherein the protector is a simple, unitary device that can be removably mounted on an individual block and jack assembly without unduly interfering with access to the connecting terminals of the assemblies.
It is a further object of the present invention to provide a simple, unitary line surge protector for connection to individual 444-type block and jack assemblies mounted in stacked relation on a main telephone distribution frame wherein the protector includes an insulative housing having no protruding electrical contacts.
It is another object of the present invention to accomplish the foregoing objects through the use of conventional molding techniques in the manufacture of the protector.
These and other objects and advantages of the present invention are accomplished through the provision of a unitary line surge protector that connects to an individual, existing 444-type block and jack assembly of a main distribution frame having multiple block and jack assemblies mounted in stacked relation on a mounting plate. The 444-type block and jack assembly includes four generally parallel connector strips and an outside clamping strip all separated from each other and the mounting plate by interposed insulating strips. The two interior connector strips and their interposed insulating strip extend outwardly beyond the mounting plate in a first direction to form first and second jack connectors. The two outside connector strips have spring extensions that also extend outwardly beyond the mounting plate in the first direction and are biased into contact with the respective first and second jack connectors to thereby form a pair of normally closed jacks. The outside clamping strip also extends outwardly along side the jacks to form a guide extension having a shoulder stop intermediate its ends.
Each of the connector strips has a right angle extension serving as a connecting lug for connection of telephone lines thereto. The connecting lugs are arranged in two wire pairs with current paths between the pairs of connecting lugs passing through the pair of normally closed jacks. The pair of normally closed jacks and guide extension are approximately equal in width in the stacking direction, and are spaced from the pair of jacks and guide extension of an immediately adjacent jack and block assembly in a stack of such assemblies by a predetermined fixed spacing.
The preferred line surge protector cooperates with an individual 444-type jack and block assembly through the provision of a flat housing of electrically insulative material having a front edge with an edge thickness greater than the width of one pair of normally closed jacks but no greater than the sum of the width of one pair of the jacks plus the fixed spacing between jacks of adjacent assemblies. The front edge of the housing is provided with apertures to receive the pair of jacks and the guide extension of one assembly.
An electrically conductive guide engaging member is disposed in the aperture receiving the guide extension. The guide engaging member is a flat strip of metal that contacts the guide extension and spring biases it into contact with an interior surface of the aperture so as to simultaneously provide an electrical contact and a force fit for the guide extension when it is inserted into the aperture. In the aperture receiving the pair of normally closed jacks there are disposed first and second pairs of electrically conductive jack engaging members. The jack engaging members are flat strips of metal that are configured to contact the jacks and spring bias the jacks into an open position.
A pair of line surge protection devices is disposed in electrically isolated cavities within the flat housing. Each protection device includes two line terminals and a ground terminal. Each pair of jack engaging members extends through electrically isolated slots in the housing into electrical contact with the respective line terminals of an associated one of the protection devices. The guide engaging member extends through an electrically isolated slot in the housing into contact with the ground terminal of each of the protection devices.
When the housing is connected to a block and jack assembly, the normally closed jacks are received in the one aperture and are opened by the engaging members in the aperture. The current path between the connecting lugs of the block and jack assembly is thereby opened and current is diverted through the jack engaging members and the protection devices in the housing. The housing is sized so that it can be connected to one block and jack assembly without interfering with access to an immediately adjacent assembly. In addition, the housing is shaped to allow access to the connecting lugs of the block and jack assemblies for soldering or the like.
The foregoing and other advantages and features of the present invention will be more fully appreciated by one skilled in the art to which the invention pertains from the following detailed description when read in conjunction with the drawings.